1. Field of the Invention
The present invention relates to a printer for printing characters, symbols, graphic patterns and images, and more particularly to a battery-operated dot-print thermal printer.
2. Description of the Prior Art
A dot-print printer which serially reads out print data from a character generator ROM and prints them under a control of a control circuit such as a microcomputer has been known. In the printer, a print unit (hereinafter referred to as a head) is mounted on a carriage and print elements of the head print dot patterns in synchronism with a timing of movement of the carriage in a print direction. In such a printer, since the dot patterns are printed with one-dot print width of the print element being equal to one-dot shift distance of the head, dots are overlapped or spaced if the dot shift distance is nonuniform when the head is moved. When an oblique pattern is printed, a smoothness of the pattern is not obtained in many cases. In a battery-operated printer, the above problems are remarkable because of a voltage variation.
In order to resolve those problems, the number of dots of a character generating ROM may be increased or a control circuit for precisely controlling the shift distance of the head may be provided. In this case, however, the lifetime of the printer battery is shortened.
In another approach, the one-dot shift distance of the head is set to be smaller than the one-dot print width of the head so that the dots are printed in an overlapped fashion. However, since the print density of each dot is constant, the dots at the opposite ends of a line of dots are of lower density than the overlapped dots and the printed characters are not sharp.